Flow generation systems can be generally described as systems that generate a gaseous flow, for example airflow or a blend of ambient air and oxygen. A ventilator is one example of a flow generation system. A ventilator is a piece of medical equipment that delivers a flow of gas, such as a blend of oxygen and ambient air to the airway of a patient to assist in or substitute a patient's breathing. Most ventilators deliver a blend of oxygen and air so that the patient receives a target oxygen concentration greater than that of ambient air. Generally, ventilators utilize a combination of single-use or reusable disposable components for the patient interface (e.g. a mask or mouthpiece connected to flexible tubing) and non-disposable capital equipment (e.g. air pumps, sensors, controller modules, humidifiers, etc.) that is used over a period of time among different patients. The patient interface can be for example a mouthpiece, mask (full face, nasal, pillow, total mask, or combinations of these), endotracheal tube or tracheostomy tube.
Although there are a variety of ventilator designs currently used in the field, most conventional designs will fall into either the single-limb or double-limb category. Single-limb ventilators typically come in different configurations. In certain types of single limb configurations, there is no “active” exhalation valve. Instead, a hole (or multiple holes) at or near the patient connection serves as a “passive” exhalation valve. However, in this configuration, since the hole(s) is not big enough to handle the entire exhalation flow, some of the exhaled flow travels back to the device. In an acute care single-limb circuit, a single tube is also used for inhalation and exhalation. Typically, a section of the tube near the patient's mouthpiece is equipped with an exhalation valve, which is switched on and off according to a pressure and/or flow signal measured by the system. The pressure and/or flow signal can detect when air is flowing from the ventilator equipment to the patient, causing the exhalation valve to stay closed. The pressure and/or flow signal can also detect when air stops flowing, or when an upstream airflow is detected, causing the exhalation valve to open. Double limb circuits are similar, except that they have a second tube connecting back to the ventilator, where the exhalation valve is located in this case. The advantage of a single limb circuit is that it eliminates the issues of added bulk, weight and production costs that are present with double limb design. However, one of the shortcomings of single-limb ventilators is cross-contamination of the ventilator, since exhaled gas from the patient can return to the dedicated or non-disposable components of the ventilator system during exhalation.
With reference now to prior art FIG. 1, a conventional single limb ventilator circuit 10 is shown in the pneumatic schematic circuit diagram. An air pump 12 is connected via an in-line gas flow circuit 20 to a humidifier 16 and a patient interface 18. The patient interface 18 can include the single-limb flexible patient tubing and a patient interface for the patient to breathe through. A flow sensor 22 and a pressure sensor 24 are positioned in the gas flow circuit 20, and they communicate measurements to a controller 14 that controls the air pump 12. As demonstrated by the diagram, the equipment in this blower based single-limb ventilator is exposed to contamination from the patient's exhaled gas.
Currently, the only recommended method in preventing cross-contamination is to add bacteria filters 42 at the ventilator outlet, as shown for example in prior art FIG. 2A. If the medical facility or patient fails to use bacteria filters, the main body of the ventilator components are exposed to the patient exhaled gas, and subsequently susceptible to contamination. In addition to the potential cross-contamination, for the cases of bacteria filter use, there are at least a couple of scenarios which could affect the proper ventilator functions. Many ventilator systems include integrated humidifiers, although some do not. Humidifiers (heated or non-heated) are usually required for patients who are on ventilators. Typically, for ventilator systems that include integrated humidifiers, the bacteria filter is located downstream of the humidifier (see for example FIG. 2A). However, one issue with locating a bacteria filter downstream of the integrated humidifier is that water vapor in the gas often leads to improper function of ventilator components, negatively affecting proper ventilator function. In the case of a ventilator system that is not equipped with an integrated humidifier, such as systems that use an external humidifier 16′ (see for example FIG. 2B), the bacterial filter 42′ can be located downstream or upstream of the external humidifier 16′. However, even for systems that utilize an external humidifier 16′, where the bacteria filter 42′ can be located between the ventilator outlet and the humidifier inlet, the chances of the bacteria filter 42′ being compromised due to the humidified gas will remain high, again affecting proper operation of the components of the ventilators. Some ventilators (or mainly sleep apnea therapy devices) are designed to be used without bacteria filters altogether (see for example FIG. 1). In this case, ventilators and their components are naturally susceptible to contamination.
Thus, what is needed in the art is a ventilator system that can more effectively utilize a bacterial filter and a humidifier while minimizing the risk of cross-contamination to dedicated ventilator components and devices.